Functionalized Asymmetric Bola-Type Amphiphiles for Efficient Gene and Drug Delivery

Drug self-delivery systems: A comprehensive review on small molecule nanodrugs

Drug self-delivery systems are nanostructures composed of a drug as the main structural unit, having the ability of intracellular trafficking with no additional carrier. In these systems, the drug itself undertakes the functional and structural roles; thereby, the ancillary role of excipients and carrier-related limitations are circumvented and therapeutic effect is achieved at a much lower dose. Such advantages -which are mainly but not exclusively beneficial in cancer treatment- have recently led to an upsurge of research on these systems. Subsequently, various terminologies were utilized to describe them, referring to the same concept with different words. However, not all the systems developed based on the self-delivery approach are introduced using one of these keywords. Using a scoping strategy, this review aims to encompass the systems that have been developed as yet -inspired by the concept of self-delivery- and classify them in a coherent taxonomy. Two main groups are introduced based on the type of building blocks: small molecule-based nanomedicines and self-assembling hybrid prodrugs. Due to the diversity, covering the whole gamut of topics is beyond the scope of a single article, and, inevitably, the latter is just briefly introduced here, whereas the features of the former group are meticulously presented. Depending on whether the drug is merely a carrier for itself or carries a second drug as cargo, two classes of small molecule-based nanomedicines are defined (i.e., pure nanodrugs and carrier-mimicking systems, respectively), each having sub-branches. After introducing each branch and giving some examples, possible strategies for designing each particular system are visually displayed. The resultant mind map can create a macro view of the taken path and its prospects, give a profound insight into opportunities, spark new ideas, and facilitate overcoming obstacles. Taken together, one can foresee a brilliant future for self-delivery systems as a pioneering candidate for the next generation of drug delivery systems.

Investigation of keratolytic impact of synthetic bolalipids on skin penetration of a model hydrophilic permeant

Synthetic single-chain bolalipids (SSCBs) are novel excipients in drug delivery, with potential as stabilizers or solubilizers. However, their impact on skin barrier function has not been comprehensively studied. Therefore, two SSCBs (PC-C24-PC and PC-C32-PC) were studied in aqueous systems for their impact on penetration of a model permeant into porcine skin. Concentrations of 0.05 - 5 % w/w were tested; PC-C24-PC formulations were low-viscosity liquids while PC-C32-PC formed viscous dispersions to gels at room temperature. Formulations were compared for their ability to enhance sodium fluorescein penetration (SF, 0.1 % w/w) into skin via tape stripping. Using NIR-densitometry, the effect of SSCB formulations on corneocyte cohesion was evaluated. Data were compared with phospholipid mixture Lipoid S-75, sodium dodecyl sulfate (SDS), and polyethylene glycol 12-hydroxystearate (PEG-HS), and distilled water as negative control. Contrary to the hypothesis, both SSCBs failed to increase SF penetration into the stratum corneum, but rather showed a significant decrease in penetration depth compared to water. Both SSCBs exhibited a keratolytic effect at 5 % w/w, leading to substantial removal of proteins from the skin surface. Consequently, SSCBs may not enhance penetration of hydrophilic drugs into skin, but could be used as keratolytic agents.

Engineering aspects of lipid-based delivery systems: In vivo gene delivery, safety criteria, and translation strategies

Defects in the genome cause genetic diseases and can be treated with gene therapy. Due to the limitations encountered in gene delivery, lipid-based supramolecular colloidal materials have emerged as promising gene carrier systems. In their non-functionalized form, lipid nanoparticles often demonstrate lower transgene expression efficiency, leading to suboptimal therapeutic outcomes, specifically through reduced percentages of cells expressing the transgene. Due to chemically active substituents, the engineering of delivery systems for genetic drugs with specific chemical ligands steps forward as an innovative strategy to tackle the drawbacks and enhance their therapeutic efficacy. Despite intense investigations into functionalization strategies, the clinical outcome of such therapies still needs to be improved. Here, we highlight and comprehensively review engineering aspects for functionalizing lipid-based delivery systems and their therapeutic efficacy for developing novel genetic cargoes to provide a full snapshot of the translation from the bench to the clinics. We outline existing challenges in the delivery and internalization processes and narrate recent advances in the functionalization of lipid-based delivery systems for nucleic acids to enhance their therapeutic efficacy and safety. Moreover, we address clinical trials using these vectors to expand their clinical use and principal safety concerns.

Self-assembly of amphiphilic amino acid derivatives for biomedical applications

Amino acids are one of the simplest biomolecules and they play an essential role in many biological processes. They have been extensively used as building blocks for the synthesis of functional nanomaterials, thanks to their self-assembly capacity. In particular, amphiphilic amino acid derivatives can be designed to enrich the diversity of amino acid-based building blocks, endowing them with specific properties and/or promoting self-assembly through hydrophobic interactions, hydrogen bonding, and/or π-stacking. In this review, we focus on the design of various amphiphilic amino acid derivatives able to self-assemble into different types of nanostructures that were exploited for biomedical applications, thanks to their excellent biocompatibility and biodegradability.

Investigating bolalipids as solubilizing agents for poorly soluble drugs: Effects of alkyl chain length on solubilization and cytotoxicity

Synthetic single-chain bolalipids with symmetrical headgroups have shown potential in various pharmaceutical applications, such as the stabilization of liposome bilayers. Despite their amphiphilic character, synthetic bolalipids have not yet been investigated for their suitability as solubilizing agents for poorly soluble drug compounds. In this study, three synthetic single-chain bolalipids with increasing alkyl chain lengths (C22, C24 and C26) were investigated. All three bolalipids were able to achieve an increased solubility of the model drug, mefenamic acid, by approximately 180% in a pH 7.4 buffer compared to only a 102-105% increase achieved by sodium dodecyl sulfate (SDS) or the non-ionic surfactant pegylated hydroxystearate (PEG-HS). Subsequently, interfacial activity of bolalipids and their ability to destabilize liposomal bilayers were investigated. The C22 bolalipid exhibited a consistently lower interfacial activity, which was consistent with its significantly lower cytotoxicity in the macrophage-like cell line, J774. A1, compared to C24 and C26 counterparts. The mean IC₅₀ values of the bolalipids tested (0.035-0.093 mM) were approximately 4-100-fold lower than that of SDS (0.401 mM) or PEG-HS (0.922 mM), with the mechanism of toxicity linked to increased cell membrane permeability, as is expected for surfactants. In summary, evidence from this study shows that decreasing the length of the bolalipid alkyl linker from C26 to C22 resulted in a significantly decreased cytotoxicity with no loss in drug solubilization efficiency.

Smart Design of Mitochondria-Targeted and ROS-Responsive CPI-613 Delivery Nanoplatform for Bioenergetic Pancreatic Cancer Therapy

Mitochondria, as the powerhouse of most cells, are not only responsible for the generation of adenosine triphosphate (ATP) but also play a decisive role in the regulation of apoptotic cell death, especially of cancer cells. Safe potential delivery systems which can achieve organelle-targeted therapy are urgently required. In this study, for effective pancreatic cancer therapy, a novel mitochondria-targeted and ROS-triggered drug delivery nanoplatform was developed from the TPP-TK-CPI-613 (TTCI) prodrug, in which the ROS-cleave thioketal functions as a linker connecting mitochondrial targeting ligand TPP and anti-mitochondrial metabolism agent CPI-613. DSPE-PEG2000 was added as an assistant component to increase accumulation in the tumor via the EPR effect. This new nanoplatform showed effective mitochondrial targeting, ROS-cleaving capability, and robust therapeutic performances. With active mitochondrial targeting, the formulated nanoparticles (TTCI NPs) demonstrate much higher accumulation in mitochondria, facilitating the targeted delivery of CPI-613 to its acting site. The results of in vitro antitumor activity and cell apoptosis revealed that the IC₅₀ values of TTCI NPs in three types of pancreatic cancer cells were around 20~30 µM, which was far lower than those of CPI-613 (200 µM); 50 µM TTCI NPs showed an increase in apoptosis of up to 97.3% in BxPC3 cells. Therefore, this mitochondria-targeted prodrug nanoparticle platform provides a potential strategy for developing safe, targeting and efficient drug delivery systems for pancreatic cancer therapy.

Self-Assembling Peptidic Bolaamphiphiles for Biomimetic Applications

Bolaamphiphile, which is a class of amphiphilic molecules, has a unique structure of two hydrophilic head groups at the ends of the hydrophobic center. Peptidic bolaamphiphiles that employ peptides or amino acids as their hydrophilic groups exhibit unique biochemical activities when they self-organize into supramolecular structures, which are not observed in a single molecule. The self-assembled peptidic bolaamphiphiles hold considerable promise for imitating proteins with biochemical activities, such as specific affinity toward heterogeneous substances, a catalytic activity similar to a metalloenzyme, physicochemical activity from harmonized amino acid segments, and the capability to encapsulate genes like a viral vector. These diverse activities give rise to large research interest in biomaterials engineering, along with the synthesis and characterization of the assembled structures. This review aims to address the recent progress in the applications of peptidic bolaamphiphile assemblies whose densely packed peptide motifs on their surface and their stacked hydrophobic centers exhibit unique protein-like activity and designer functionality, respectively.

Synthesis and aggregation behaviour of single-chain, 1,32-alkyl-branched bis(phosphocholines) - part 2: lateral chain length triggers self-assembling from sheets to fibres to vesicles

Six single-chain, 1,32-alkyl-branched bis(phosphocholines) PC-C32(1,32Cm)-PC have been synthesized as model lipids for naturally occurring archaeal membrane lipids. The preparation of these bipolar amphiphiles bearing lateral alkyl chains of different lengths (C4-C15) was realized using a Cu-catalyzed Grignard bis-coupling reaction of various primary alkyl-branched bromides as side parts and a 1,22-dibromide as the centre part. The aggregation behaviour of these bolalipids in water was initially investigated by differential scanning calorimetry and transmission electron microscopy. As a main result, the types of aggregates found and their stability upon heating were strongly connected to the length of the lateral alkyl chain of the bolalipid: short and long lateral chains led to lamellar structures, whereas side chains of medium length led to fibrous aggregates. In future, these bolalipids could be used to produce tailored and stabilized liposomes for oral drug delivery.

Biomedically Relevant Applications of Bolaamphiphiles and Bolaamphiphile-Containing Materials

Bolaamphiphiles (BAs) are structurally segmented molecules with rich assembly characteristics and diverse physical properties. Interest in BAs as standalone active agents or as constituents of more complex therapeutic formulations has increased substantially in recent years. The preorganized amphiphilicity of BAs allows for a range of biological activities including applications that rely on multivalency. This review summarizes BA-related research in biomedically relevant areas. In particular, we review BA-related literature in four areas: gene delivery, antimicrobial materials, hydrogels, and prodrugs. We also discuss several distinguishing characteristics of BAs that impact their utility as biomedically relevant compounds.

Thermoresponsive Structure and Dye Encapsulation of Micelles Comprising Bolaamphiphilic Quercetin Polyglycoside

A bolaamphiphile is a special member of amphiphilic molecules, which contains a hydrophobic skeleton and two water-soluble groups on both ends. Bolaamphiphiles form thermally stable associates in water under lower concentration than those of typical monoheaded amphiphiles, indicating the potential usefulness of bolaamphiphiles as the component of nanomaterials. However, the structural diversity of bolaamphiphiles is limited at this moment. We recently developed the synthesis of quercetin-3-O-polyglycoside (QP) as a new entry of bolaamphiphiles via a one-pot polymerization using sugar-based cyclic sulfite initiated by quercetin skeleton. Herein, we show the bolaamphiphilic properties of QP in detail. The micellization behaviors of QP are systematically investigated through comparison with those of quercetin (Que) and isoquercitrin (IQ) to evaluate the roles of glycone on the micellization of quercetin derivatives. The morphology of the micelles bearing QP is observed by cryo-transmission electron microscopy (cryo-TEM), suggesting the formation of bolaamphiphile-specific giant ribbon-like micelles in addition to spherical micelles. The thermoresponsive micellization behaviors are also discussed through the critical micelle concentration (CMC) values, the dynamic light scattering analyses at various temperatures, and thermal hysteresis of the micellizations. It is indicated that the polysaccharide chains integrated on the surface of micelles would serve as a steric protecting group to endow the micelles with kinetic stability. These results will shed light on natural glycoside skeletons to design a new class of micelles for advanced health applications in near future.

Zinc(ii)-cyclen coordinative amphiphiles for enhanced gene delivery

In this study, we developed coordinative amphiphiles for use as novel non-viral DNA vectors. As a modification of a conventional cationic lipid structure, we replaced the cationic head with a zinc(ii)-1,4,7,10-tetraazacyclododecane (Zn-cyclen) complex as a phosphate-directing group, and used biocompatible skeletons (α-tocopherol or cholesterol) as hydrophobic tails. The structure-activity relationship (SAR) was systematically investigated to study the effect of Zn-coordination on the gene transfection between cyclen-based traditional head-tail lipids and Zn(ii)-cyclen coordinative amphiphiles. The results reveal that both Zn-free lipids and Zn-containing amphiphiles could condense DNA into nano-sized particles with appropriate size and zeta-potentials. Agarose gel retardation assay and MTS-based cell viability assays demonstrated that the Zn(ii)-cyclen complex exhibited slightly lower DNA binding ability and much lower cytotoxicity compared to liposome analogues, respectively. Most importantly, in vitro transfection studies showed that the coordination of zinc(ii) to cyclen may dramatically increase the transfection efficiency of the conventional cationic lipid, and α-tocopherol-containing coordinative amphiphile Zn-Cyc-Toc gives the best transfection efficiency, which was enhanced 24.4 times after coordination and was 6.1 times higher than commercial transfection reagent lipofectamine 2000. Mechanism studies confirmed that the DNA complex formed from Zn-Cyc-Toc might induce higher cellular uptake and better endosomal escape ability than the lipoplexes formed from Zn-free lipid Cyc-Toc. This study not only demonstrates that these coordinative amphiphiles might be promising non-viral gene vectors, but also presents a novel strategy to enhance the gene transfection efficiency and biocompatibility of cyclen-based cationic lipids.

Zn-coordination could dramatically enhance the gene transfection efficiency and reduce the cytotoxicity of conventional cyclen-based cationic liposomes.

A Non-Viral Plasmid DNA Delivery System Consisting on a Lysine-Derived Cationic Lipid Mixed with a Fusogenic Lipid

The insertion of biocompatible amino acid moieties in non-viral gene nanocarriers is an attractive approach that has been recently gaining interest. In this work, a cationic lipid, consisting of a lysine-derived moiety linked to a C12 chain (LYCl) was combined with a common fusogenic helper lipid (DOPE) and evaluated as a potential vehicle to transfect two plasmid DNAs (encoding green fluorescent protein GFP and luciferase) into COS-7 cells. A multidisciplinary approach has been followed: (i) biophysical characterization based on zeta potential, gel electrophoresis, small-angle X-ray scattering (SAXS), and cryo-transmission electronic microscopy (cryo-TEM); (ii) biological studies by fluorescence assisted cell sorting (FACS), luminometry, and cytotoxicity experiments; and (iii) a computational study of the formation of lipid bilayers and their subsequent stabilization with DNA. The results indicate that LYCl/DOPE nanocarriers are capable of compacting the pDNAs and protecting them efficiently against DNase I degradation, by forming Lα lyotropic liquid crystal phases, with an average size of ~200 nm and low polydispersity that facilitate the cellular uptake process. The computational results confirmed that the LYCl/DOPE lipid bilayers are stable and also capable of stabilizing DNA fragments via lipoplex formation, with dimensions consistent with experimental values. The optimum formulations (found at 20% of LYCl content) were able to complete the transfection process efficiently and with high cell viabilities, even improving the outcomes of the positive control Lipo2000*.

Lipoaminoacids Enzyme-Based Production and Application as Gene Delivery Vectors

Biosurfactant compounds have been studied in many applications, including biomedical, food, cosmetic, agriculture, and bioremediation areas, mainly due to their low toxicity, high biodegradability, and multifunctionality. Among biosurfactants, the lipoplexes of lipoaminoacids play a key role in medical and pharmaceutical fields. Lipoaminoacids (LAAs) are amino acid-based surfactants that are obtained from the condensation reaction of natural origin amino acids with fatty acids or fatty acid derivatives. LAA can be produced by biocatalysis as an alternative to chemical synthesis and thus become very attractive from both the biomedical and the environmental perspectives. Gemini LAAs, which are made of two hydrophobic chains and two amino acid head groups per molecule and linked by a spacer at the level of the amino acid residues, are promising candidates as both drug and gene delivery and protein disassembly agents. Gemini LAA usually show lower critical micelle concentration, interact more efficiently with proteins, and are better solubilising agents for hydrophobic drugs when compared to their monomeric counterparts due to their dimeric structure. A clinically relevant human gene therapy vector must overcome or avoid detect and silence foreign or misplaced DNA whilst delivering sustained levels of therapeutic gene product. Many non-viral DNA vectors trigger these defence mechanisms, being subsequently destroyed or rendered silent. The development of safe and persistently expressing DNA vectors is a crucial prerequisite for a successful clinical application, and it one of the main strategic tasks of non-viral gene therapy research.

GSH/pH dual-responsive biodegradable camptothecin polymeric prodrugs combined with doxorubicin for synergistic anticancer efficiency

GSH and pH dual-responsive camptothecin polymeric prodrugs combined doxorubicin for synergistic drug delivery to highly improved selectivity and synergy benefiting from good long-term stability, better internalization and sensitive dual-responsibility.

A Gemini Cationic Lipid with Histidine Residues as a Novel Lipid-Based Gene Nanocarrier: A Biophysical and Biochemical Study

This work reports the synthesis of a novel gemini cationic lipid that incorporates two histidine-type head groups (C₃(C16His)₂). Mixed with a helper lipid 1,2-dioleoyl-sn-glycero-3-phosphatidyl ethanol amine (DOPE), it was used to transfect three different types of plasmid DNA: one encoding the green fluorescence protein (pEGFP-C3), one encoding a luciferase (pCMV-Luc), and a therapeutic anti-tumoral agent encoding interleukin-12 (pCMV-IL12). Complementary biophysical experiments (zeta potential, gel electrophoresis, small-angle X-ray scattering (SAXS), and fluorescence anisotropy) and biological studies (FACS, luminometry, and cytotoxicity) of these C₃(C16His)₂/DOPE-pDNA lipoplexes provided vast insight into their outcomes as gene carriers. They were found to efficiently compact and protect pDNA against DNase I degradation by forming nanoaggregates of 120⁻290 nm in size, which were further characterized as very fluidic lamellar structures based in a sandwich-type phase, with alternating layers of mixed lipids and an aqueous monolayer where the pDNA and counterions are located. The optimum formulations of these nanoaggregates were able to transfect the pDNAs into COS-7 and HeLa cells with high cell viability, comparable or superior to that of the standard Lipo2000*. The vast amount of information collected from the in vitro studies points to this histidine-based lipid nanocarrier as a potentially interesting candidate for future in vivo studies investigating specific gene therapies.